1 An Introduction to UML Interaction (Sequence and Communication) Diagrams Georgia State University CIS 3300 Spring, 2009

Models, Views, and Diagrams Use Case Diagrams Use Case Diagrams Use Case Diagrams Scenario Diagrams Scenario Diagrams Communication Diagrams State Diagrams State Diagrams Component Diagrams Component Diagrams Component Diagrams Deployment Diagrams State Diagrams State Diagrams Object Diagrams Scenario Diagrams Scenario Diagrams State Machine Diagrams Use Case Diagrams Use Case Diagrams Sequence Diagrams State Diagrams State Diagrams Class Diagrams Activity Diagrams A model is a complete description of a system from a particular perspective Models

3 Behavioral Diagrams Used to visualize, specify, construct, document dynamic aspects of system: use case diagram sequence diagram communication diagram state machine diagram activity diagram

4 Diagramming Scenarios: UML ways of expressing scenarios Activity diagrams Several scenarios (even a full use case) at once Similar to Petri nets, Graphcet, (concurrent) flow charts… Interaction (sequence and communication) diagrams Only one scenario per diagram Involve/introduce (high level) objects Sequence diagram Accent on the time flow Communication diagram Accent on the messages between objects

5 Interaction Diagrams (Sequence and Communication) Describe how groups of objects collaborate in some behavior Sequence diagrams Time-oriented Communication diagrams Message-oriented

6 Diagramming Scenarios: Sequence Diagrams Describe one scenario Involve objects and messages Shows a number of objects and the messages that are passed between these objects. Accent is on the time flow of events

7 Simple scenario: Diagramming Scenarios: Sequence Diagrams We have an order and are going to invoke a command on it to calculate its price. To do that, the order needs to look at all the line items on the order and determine their prices, which are based on the pricing rules of the order’s line products. Having done that for all the line items, the order then needs to compute an overall discount, which is based on rules tied to the customer.

10 Sequence Diagrams UML 1.0 versus UML 2.0: Objects pass messages (UML 1.0) Participants pass messages (UML 2.0) Show how participants (objects) interact. Differences in interaction styles: Fig 4-1: Centralized, e.g. one participant does all the processing and other participants supply data. Fig 4-2: Distributed, e.g. processing is split among many participants.

11 Diagramming Scenarios: Sequence Diagrams (cont.) get_Customer_Information() select_transaction(sel) display_menu() quit Customer Bank time card_taken eject_card card_returned insert_card ATM Session « new » Transaction « new » display_menu()

12 Interaction and Message An interaction is a behavior that comprises a set of messages, exchanged among a set of objects, to accomplish a specific purpose. A message is the specification of a communication between objects that conveys information, with the expectation that some kind of activity will ensue.

13 Sequence Diagram A sequence diagram is an interaction diagram that emphasizes the time ordering of messages. A lifeline is a vertical dashed line that represents the lifetime of an object. A focus of control is a tall, thin rectangle that shows the period of time during which an object is performing an action.

14 Sequence Diagram Notation

15 Sequence Diagram Notation

16 Sequence Diagram Notation

17 Sequence Diagram Captures dynamic behavior (time- oriented) Purpose Model flow of control Illustrate typical scenarios

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UML Sequence Diagrams Used during requirements analysis To refine use case descriptions to find additional objects (“participating objects”) Used during system design to refine subsystem interfaces Classes (and objects) are represented by columns Messages are represented by arrows Activations are represented by narrow rectangles Lifelines are represented by dashed lines selectZone() pickupChange() pickUpTicket() insertCoins() Passenger TicketMachine

UML Sequence Diagrams: Nested Messages The source of an arrow indicates the activation which sent the message An activation is as long as all nested activations selectZone() Passenger ZoneButton TarifScheduleDisplay lookupPrice(selection) displayPrice(price) price Dataflow …to be continued...

21 Sequence Diagram Observations UML sequence diagram represent behavior in terms of interactions. Complement the class diagrams which represent structure. Useful to find participating objects. Time consuming to build but worth the investment.

22 Diagramming Scenarios: Communication Diagrams Describe one scenario Involve objects and messages Accent is on messages exchanged between objects Sequence and Communication diagrams are largely equivalent.

23 Diagramming Scenarios: Communication Diagrams (cont.) : Customer : ATM : Bank : Session : Transaction 1: insert_card 7: card_taken 4: select_transaction 3: get_customer_information 5: « create »2: « create » 6: eject_card

24 Communication Diagram A communication diagram is an interaction diagram that emphasizes the organization of the objects that participate in the interaction. A path is a link between objects, perhaps with a stereotype such as «local» attached. Sequence numbers indicate the time ordering of messages, to one or more levels.

25 Communication Diagram Captures dynamic behavior (message- oriented) Purpose Model flow of control Illustrate coordination of object structure and control

26 Communication Diagram Notation

27 Communication Diagram Notation

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